THE EFFECTS OF MERCURIC CHLORIDE ON CULTURED ATLANTIC SPOTTED DOLPHIN (Stenella plagiodon) RENAL CELLS AND THE ROLE OF SELENIUM IN PROTECTION

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Abstract

Marine mammals are known for their low susceptibility to mercury toxicity, and it was hypothesized that selenium may play a role in protection against mercury toxicity. To gain insight into the mechanisms of the low susceptibility of cetaceans, we investigated the in vitro effects (1) of mercuric chloride (HgCl2) on the ultrastructure and cell death of Atlantic spotted dolphin renal cells (Sp1K cells), (2) of HgCl2 on the cell proliferation and cell cycle status of Sp1K and Rhesus monkey renal cells (MK2), and (3) of sodium selenite (Na2SeO3) on cell proliferation and cell death of control and HgCl2-treated Sp1K cells.
HgCl2 affected multiple organelles and nuclei in Sp1K cells, and induced apoptosis in a time-and dose-dependent manner. Both ultrastructural changes and induction of apoptosis were milder than seen in other cell types in previous publications. In addition, Sp1K cells were able to proliferate at 25 ÂµM HgCl2 while MK2 cells were killed at 15 ÂµM HgCl2. An increase in percentage of cells in the G0/G1 phase in the cell cycle and a decrease in S, and G2/M phase cells were seen in Sp1K cells exposed to more than 10 uM HgCl2 more than 72 hours. MK2 cells showed cell cycle changes only at 24 hours exposure, and may be due to a sensitive subgroup. These data suggested that Sp1K cells were less suscepable than other cell types in a cell-specific way, which was independent of selenium protection.
Concurrent exposure to Na2SeO3 provided protection against the HgCl2-induced decrease in cell proliferation of Sp1K. The protective effects were greater if Na2SeO3 and HgCl2 were premixed, but disappeared if exposures did not overlap. Although pretreatments with Na2SeO3 alone did not provide protection, they increased the protection of selenium administered later. Furthermore, Na2SeO3 decreased HgCl2-induced apoptosis. These data demonstrated the Na2SeO3 protection against HgCl2 toxicity in Sp1K cells in terms of cell proliferation and apoptosis.
This study is the first report that reveals the existence of mercury-selenium antagonism in cultured cetacean cells. The data supported the hypothesis that selenium protection against mercury toxicity is, at least partially, through competition of binding sites and formation of mercury-selenium complex.